Fuel cell and fuel cell stack

ABSTRACT

In a solid polymer electrolyte membrane type fuel cell of the invention, where a pair of electrodes are provided on opposite sides of a solid polymer electrolyte membrane, and the outside thereof is clamped by a pair of separators, and nonconductive picture frame-shaped members  61  are arranged at the outer edge portions of the separators, for allowing increase and decrease of a space between separators, while sealing a gap between the separators.

RELATED APPLICATIONS

This application is a Divisional application of U.S. patent applicationSer. No. 10/058,657 filed Jan. 28, 2002 (allowed), which claims priorityto Japanese Patent Application No. 2001-022047 filed 30 Jan. 2001 andJapanese Patent Application No. 2002-005333 filed 11 Jan. 2002 in Japan.The contents of the aforementioned applications are hereby incorporatedby reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a solid polymer electrolyte membranetype fuel cell, and a fuel cell stack constituted by stacking aplurality of said fuel cell units, and more specifically relates to atechnique effective in absorbing increase and decrease in the stackingdirection of separators.

2. Description of the Related Art

Fuel cells include a solid polymer electrolyte membrane type fuel cellconstituted by providing a pair of electrodes on opposite sides of thesolid polymer electrolyte membrane and sandwiching the outside thereofby a pair of separators.

In this fuel cell, a channel for a fuel gas (for example hydrogen) isprovided on the whole surface of a separator provided facing oneelectrode, a channel for an oxidant gas (for example air includingoxygen) is provided on the whole surface of a separator provided facingthe other electrode, and a channel for a cooling medium is provided oneither one of the surface of separators opposite to a surface facing theelectrode.

When the fuel gas is supplied to the reaction surface of one electrode,hydrogen is ionized, and moves to the other electrode via the solidpolymer electrolyte membrane. Electrons generated during the reactionprocess are taken out to an external circuit, and are used asdirect-current electric energy.

Since the oxidant gas is supplied to the other electrode, the hydrogenions, the electrons and the oxygen react with each other to therebygenerate water.

The surface on the opposite side of the electrode reaction plane of theseparator is cooled by the cooling medium flowing between theseparators.

Since these reactant gas and cooling medium should flow in respectivelyindependent channels, a sealing technique, which separates each channel,is important.

The portions to be sealed include; the peripheries of communicationholes formed penetrating through the separator so as to distribute andsupply the reactant gas and the cooling medium to each fuel cell unit inthe fuel cell stack, the outer peripheries of membrane electrodeassembly formed of the solid polymer electrolyte membrane and a pair ofelectrodes arranged on opposite sides thereof, the outer peripheries ofa coolant passage plane of the separator, and the outer peripheries offront and back faces of the separator. As the sealing material, aelastic and adequately resilient material, for example, an organicrubber, is adopted.

In the case where the fuel cells are stacked in a plurality of numbersto construct the fuel cell stack, and this fuel cell stack is mounted ina vehicle, there may be a case where drops of water splash and the fuelcell becomes wet, depending on the installed position, or dust entersinto the gap between separators.

However, the sealing material can prevent such water and dust fromentering into the reactant gas channel or into the cooling mediumchannel.

At the time of stacking the separators, if there is a difference inthickness between the membrane electrode assembly, or if there isbending or distortion in the separator (particularly, in a thinseparator made of metal), or if the compressive load applied from theopposite ends of the fuel cell stack is non-uniform, the separators arenot stacked parallel with each other, and inclination or warp occurs.Hence, the compression amount of each sealing material becomes unequal,and as a result, sealability deteriorates in sealing material having asmall amount of compression.

At the time of stacking the separators, it is also difficult to stackthese separators accurately without shifting their relative positionsalong the electrode reaction plane.

As measures against the above problems, there can be considered a methodin which foreign substance is prevented from entering into the gapbetween the separators, and the separators are stacked parallel witheach other, by providing, for example, a picture frame-shaped membermade of resin, at the outer edge of the separator.

Techniques similar to this are disclosed in, for example, JapaneseUnexamined Patent Application, First Publication Nos. Hei 10-74530, Hei7-249417 and Sho 61-279069.

However, if the sealing material or the membrane electrode assemblyshrinks in the stacking direction of the separators due to deteriorationwith the lapse of time, or the fuel cell expands or contracts due to theinfluence of heat or the like, the following problems will occur.

For example, when the protruding height of the sealing material from theseparator becomes lower than the protruding height of the pictureframe-shaped member, shrinkage of the space between separators isrestricted by the picture frame-shaped member. Hence, a gap may becaused between the separator and the sealing material or the membraneelectrode assembly, thereby causing a decrease in the power generationperformance, and consequently causing a situation where power generationis not possible.

On the other hand, if the space between separators expands due to theinfluence of heat or the like, a sealing material such as a rubber willbe resiliently restored and extend in the stacking direction of theseparators, and hence, this sealing material can follow the expansion ofthe space between separators without separating from the separator, tosome extent. A picture frame-shaped member made of resin or the like,however, since this does not expand in the stacking direction of theseparators, this cannot accommodate the expansion of the space betweenseparators.

Therefore, a gap occurs between the picture frame-shaped members, andforeign substance may enter there.

Moreover, it is desired to prevent a liquid connection by the coolingmedium, which causes an electric current flowing through the coolingmedium, and it is also necessary to prevent adjacent separators in thereactant gas channel from being electrically short circuited.

Particularly, in the case of a fuel cell using thin metal separators,since the space between separators is small, it is particularly desiredto specially take measures to prevent electrical short circuited fromoccurring between adjacent separators, taking into account that foreignsubstance such as dust and carbon particles become mixed in the reactantgas.

SUMMARY OF THE INVENTION

In order solve above-described problems, the fuel cell of the presentinvention is constituted as follows.

According to the first aspect of the present invention, a fuel cellcomprising a pair of separators which clamp outsides of a pair ofelectrodes (for example, electrodes 9 in the embodiment) provided onboth sides of a solid polymer electrolyte membrane (for example, thesolid polymer electrolyte membrane 7 in the embodiment), wherein thefuel cell further comprises a nonconductive picture frame-shaped member(for example, picture frame-shaped members 61, 81, 91, 101, 121, 131,141, 251 and 261 in the embodiments) which allows increasing anddecreasing of a space between separators, while sealing the gap betweenseparators, is provided at the outer edge of said separator.

According to this construction, with respect to a movement increasingthe space between separators, a gap is not produced between theseparator and the picture frame-shaped member, and furthermore, withrespect to a movement narrowing the space between separators, thismovement is not restricted by the picture frame-shaped member.

According to the second aspect of the present invention, in a fuel cellaccording to the first aspect, said picture frame-shaped members (forexample, picture frame-shaped members 101, 111, 121, 131 in theembodiments) are constituted so as to be able to slide relative to eachother.

According to the above construction, the width of the space betweenseparators can be mechanically adjusted by relative sliding movement ofthe picture frame-shaped members.

According to the third aspect of the present invention, in the fuel cellaccording to the first aspect, said separator is made of a metal, andsaid picture frame-shaped member (for example, picture frame-shapedmembers 61, 81, 91, 261 in the embodiments) is formed of a hard material(for example, main body portions 61 a, 81 a, 91 a, and 261 a in theembodiment) and a elastic material (increase and decrease absorbingportions 61 b, 81 b, 91 b, and 261 b in the embodiment).

According to the above construction, since the elastic material iscapable of elastically contracting in the stacking direction of the fuelcell, separators are not limited in access to each other.

The expansion of spaces between separators in proximity can beaccommodated by the elastic material due to resilient contractionthereof in the stacking direction.

According to the fourth aspect of the present invention, in the fuelcell according to the first aspect, said picture frame-shaped membercomprises a separator positioning device (for example, a combination ofa concave portion 123 and a convex portion 125, a combination of an endsurface 131A and an end surface 131B, and a combination of a groovedportion with a triangular cross-section 143 and a protruded portion 145with a triangular cross-section 145 in the embodiments).

According to the above construction, it is possible to prevent relativemisalignment between separators that may occur when the separators arestacked.

According to the fifth aspect of the present invention, in the fuel cellaccording to the first aspect, the outer peripheries of the separatorsare covered with the picture frame-shaped members (for example, pictureframe-shaped members 61, 81, 91, 101, 111, 121, 131, 141, 251, and 261in the embodiments).

According to the above structure, it is possible to prevent adjacentseparators from being short circuited.

According to the sixth aspect of the present invention, in the fuel cellaccording to the fifth aspect, an reaction surface peripheral sealingmember (for example, the peripheral sealing member 52 in the embodiment)is provided for covering the reaction surfaces of separators and theoutside portion of the reaction surface peripheral sealing member istotally covered by an insulating outer edge member (for example, anincrease and decrease absorbing portion 261 b in the embodiment) isprovided around a communication hole formed in the separator.

According to the above structure, since the exposed metal surfaceoutside of the reaction surface peripheral sealing member of theseparators is totally covered by the insulating outer surface member,the corrosion resistance of the separators is improved and theelectrical short circuiting between separators can be effectivelyprevented.

According to the seventh aspect of the present invention, in the fuelcell according to the sixth aspect, both outside surfaces of thereaction surface peripheral sealing member (for example, the peripheralsealing member 52 in the embodiment) are totally covered by aninsulating outer peripheral member (for example, increase and decreaseabsorbing member 261 b), which is integrally constructed with thereaction surface peripheral sealing member.

According to the above construction, since the exposed metal surfaces atthe outer area of both surfaces at the peripheral area of the reactionsurface peripheral sealing member exposed outside of the reaction outersurface sealing member are totally covered by the insulating outersurface member, it is possible for separators to be more resistant tocorrosion, and to short circuiting between adjacent separators.

According to the eighth aspect of the present invention, in the fuelcell according to the seventh aspect, one of the reaction surfaceperipheral sealing member of adjacent separators is formed in a flatshape, and the other reaction surface peripheral sealing member whichfaces to the flat reaction surface peripheral sealing member is formedso as to protrude.

According to the above construction, since outer surfaces of thereaction surface peripheral sealing members are formed in combination offlat and protruded areas, so that the relative misalignment of the flatsurface of an reaction surface peripheral sealing member can be absorbedby the protruded surface of the other reaction surface peripheralsealing member.

According to the ninth aspect of the present invention, in the fuel cellstack according to the eighth aspect, which is constituted by aplurality of stacked fuel cell units, the picture frame-shaped membersallow expansion or contraction of spaces between separators, whilesealing the space between respective separators.

According to the above construction, for not only a single fuel cell butalso for a plurality of adjacent fuel cells, it is possible to prohibitgenerating a space between a separator and the picture frame-shapemember, and contraction of the space between separators is notprohibited by the picture frame-shape member.

According to the tenth aspect of the present invention, in the solidpolymer electrolyte membrane-type fuel cell, comprising a pair ofelectrodes formed on both surfaces of the solid polymer electrolytemembrane and a pair of metal foil separators covering both surfaces ofthe membrane-type fuel cell, insulating members (for example, insulatingmembers 201, 211, 221, 231, 241, and 271 in the embodiment) are providedaround communication holes (for example, an inlet side oxidizing agentcommunication hole 41 a, an outlet side oxidizing agent gascommunication hole 41 b, an inlet side fuel gas communication hole 43 b,an inlet side fuel gas communication hole 42 b, an inlet side coolingmedium communication hole 43 a, and an outlet side communication hole 43b in the embodiment) formed in the separators.

According to the above construction, it is possible to prevent liquidconnection by the cooling medium and to prevent short circuiting betweenadjacent separators in the reactant gas channel.

According the eleventh aspect of the present invention, in the fuel cellaccording to the tenth aspect, respective spaces (for example, the space203 in the embodiment) are provided between each two insulating membersof the adjacent separators (for example, insulating member 201 in theembodiment) in the stacking direction of the separators.

According to the above construction, the increase and decrease of theseparator spaces can be absorbed by the gap in the stacking direction ofseparators.

According to the twelfth aspect of the present invention, in the fuelcell according to the tenth aspect, each insulating member (for example,the insulating member 201 in the embodiment) of respective adjacentseparators is formed such that adjacent separators are capable ofrelatively sliding to allow increase and decrease of the space betweenseparators while the insulating members are sealing the spaces betweenseparators.

According to the above construction, increase and decrease of theseparator spaces can be mechanically absorbed by relative sliding ofrespective insulating members.

According to the thirteenth aspect of the present invention, in the fuelcell according to the tenth aspect, the insulating members (for example,the insulating member 231 and 241 in the embodiments) are made ofelastic material.

According to the above construction, contraction of the separator spacesare not regulated because the soft material is capable of resilientlycontracting in the stacking direction of the fuel cells, and expansionof the separator space can be followed by the resilient restoration ofthe elastic material due to resilient elongation of the elasticmaterial.

According to the fourteenth aspect of the present invention, in the fuelcell according to the tenth aspect, the inner peripheral surfaces of thecommunication holes are covered by the insulating member (for example,the insulating members 201, 211, 221, 231, 241, and 271 in theembodiments).

According to the above construction, it is possible to prevent shortcircuiting between inner peripheral end faces of the communication holesin the adjacent separators.

According to the fifteenth aspect of the present invention, in the fuelcell according to the tenth aspect, one of the insulating members of oneof the adjacent separators (for example, a flat portion 271 b of theinsulating member in the embodiments) is formed in a flat shape, and theinsulating member (for example, a protruded portion 271 a of theinsulating member in the embodiments) of one of insulating members ofanother separator facing to the former flat insulating member is formedso as to protrude.

According to the above construction, provision of a combination of theinsulating members of a separator into flat and protruded areas makes itpossible to absorb the relative misalignment of the protruded insulatingmember with respect to the flat insulating member.

According to the sixteenth aspect of the present invention, in the fuelcell according to the fifteenth aspect, provided with a reaction surfaceperipheral sealing member (for example, the peripheral sealing material52), one of the reaction surface peripheral sealing members of adjacentseparators (for example, the flat portion of the peripheral sealingmaterial 52 b in the embodiments) is formed in a flat shape, and theother one of the reaction surface peripheral sealing members of theopposing adjacent separators is formed so as to protrude.

According to the above construction, since the reaction surfaceperipheral sealing members are formed in a combination of flat andprotruded areas, the relative misalignment of the protruded reactionsurface peripheral sealing member corresponding to the flat outerreaction surface member cab be absorbed.

According to the seventeenth aspect of the present invention, in thefuel cell according to the sixteenth aspect, the outside portion of thereaction surface peripheral sealing members (the outer peripheralsealing material 52 in the embodiments) is totally covered by theinsulating member (for example, the insulating member 271 in theembodiment).

According to the above construction, since the exposed metal portion ofthe separators at the outside portion of the reaction surface peripheralsealing member are totally covered by the insulators, it is possible toimprove the corrosion resistance of the separators and it is possible toprevent adjacent separators from being electrically short circuited.

According to the eighteenth aspect of the present invention, in the fuelcell according to the seventeenth aspect, the reaction surfaceperipheral sealing member (for example, the peripheral sealing member 52in the embodiments) and the insulating member (for example, theinsulating member 271 in the embodiment) are integrally constituted.

According the above construction, it is possible to form the reactionsurface peripheral sealing member and the insulating member can beintegrally formed therewith.

According to the nineteenth aspect of the present invention, in the fuelcell according to the sixteenth aspect, both outside surfaces of thereaction surface peripheral sealing member (for example, the outersurface sealing member 52 in the embodiments) are covered by theinsulating outer peripheral member (for example, the insulating member271 in the embodiments) constituted integrally with the reaction surfaceperipheral sealing member.

According to the above construction, since both surfaces of the exposedmetal surfaces at the outside portion of the reaction surface peripheralsealing member are covered by the insulating members, the corrosionresistance of separators is improved and the electrical short circuitingbetween adjacent separators can be avoided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view showing a separator of a solid polymer electrolytemembrane type fuel cell according to a first embodiment of the presentinvention.

FIG. 2 is a cross-section obtained by sectioning a fuel cell stackformed by stacking a plurality of solid polymer electrolyte membranefuel cells comprising the separators in FIG. 1, at a positioncorresponding to line A-A in FIG. 1.

FIG. 3A is a cross-section showing the main parts of a modificationexample of the first embodiment, and FIG. 3B is a cross-section alongline B-B in FIG. 3A.

FIG. 4 is a cross-section showing the main parts of another modificationexample in the first embodiment.

FIG. 5 is a cross-section showing the main parts of a second embodimentof the present invention.

FIG. 6 is a cross-section showing the main parts of a modificationexample of the second embodiment.

FIG. 7 is a cross-section showing the main parts of another modificationexample in the second embodiment.

FIG. 8 is a cross-section showing the main parts of a third embodimentof the present invention.

FIG. 9 is a cross-section showing the main parts of a modificationexample of the third embodiment.

FIG. 10 is a cross-section showing the main parts of anothermodification example in the third embodiment.

FIG. 11 is a cross-section showing the main parts of a fourth embodimentof the present invention.

FIG. 12 is a cross-section showing the main parts of a modificationexample of the fourth embodiment.

FIG. 13 is a cross-section showing the main parts of anothermodification example in the fourth embodiment.

FIG. 14 is a cross-section showing the main parts of a fifth embodimentof the present invention.

FIG. 15 is a cross-section showing the main parts of a modificationexample of the fifth embodiment.

FIG. 16 is a cross-section showing the main parts of a sixth embodimentof the present invention.

FIG. 17 is a cross-section showing the main parts of a modificationexample of the sixth embodiment.

FIG. 18A is a diagram showing main portions of the other modificationexample of the first embodiment, and 18B shows an enlarged diagram ofthe protruded portion 52 a of the peripheral sealing material.

FIG. 19A is a diagram showing the main portion of the fifth embodiment,and 19B is an enlarged diagram of the protruded portion of theperipheral sealing material.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, embodiments of the present invention will be described withreference to the attached drawings.

FIG. 1 is a plan view showing a separator 3 constituting a solid polymerelectrolyte membrane type fuel cell 1 according to a first embodiment.

The fuel cell 1 is constructed by alternately stacking the separators 3and an membrane electrode assembly 5 formed by sandwiching a solidpolymer electrolyte membrane 7 by a pair of electrodes 9, as shown inFIG. 2, and a fuel cell stack is formed by stacking a plurality of unitfuel cells 1.

As shown in FIG. 1, the separator 3 comprises a corrugated sheet portion33 in which a plurality of concave portions 31 having a certain heightare formed at a certain pitch by press molding a stainless steel platematerial having a plate thickness of from 0.2 to 0.5 mm, and a planeportion 35 for mutually contacting edge portions located outside of eachcorrugated sheet portion 33 through a sealing material.

This separator 3 is provided with an inlet side oxidant gascommunication hole 41 a for passing an oxidant gas therethrough and aninlet side fuel gas communication hole 42 a for passing a fuel gastherethrough, on the upper side at opposite ends in the horizontaldirection located at the outer peripheral portion in that plane. Theseparator 3 is further provided, at the center at opposite ends in thehorizontal direction, with an inlet side cooling medium communicationhole 43 a for passing a cooling medium therethrough, and an outlet sidecooling medium communication hole 43 b for passing the used coolingmedium therethrough.

There are also provided in the separator 3 an outlet side oxidant gascommunication hole 41 b for passing the oxidant gas therethrough and anoutlet side fuel gas communication hole 42 b for passing the fuel gastherethrough, on the lower side at opposite ends in the horizontaldirection located at the outer peripheral portion in that plane, so thatthese are at diagonally opposite positions with respect to the inletside oxidant gas communication hole 41 a and the inlet side fuel gascommunication hole 42 a, respectively.

In the separator 3 on a cathode side shown in FIG. 1, the oxidant gasflows in from the inlet side oxidant gas communication hole 41 a, andthen flows into each concave portion 31 in the corrugated sheet portion33, to be directed from one short edge side of the separator towards theother short edge side thereof, and flows out from the outlet sideoxidant gas communication hole 41 b.

Similarly, in the separator 3 on an anode side (the plan view is notshown), the fuel gas flows in from the inlet side fuel gas communicationhole 42 a, and then flows into each concave portion 31 in the corrugatedsheet portion 33, to be directed from one short edge side of theseparator towards the other short edge side thereof, and flows out fromthe outlet side fuel gas communication hole 42 b.

The above described inlet side oxidant gas communication hole 41 a,inlet side fuel gas communication hole 42 a, inlet side cooling mediumcommunication hole 43 a, outlet side oxidant gas communication hole 41b, outlet side fuel gas communication hole 42 b and outlet side coolingmedium communication hole 43 b respectively correspond to communicationholes according to the present invention.

On the front face and the back face of the separator 3, there arearranged a first sealing material 51 surrounding the outside of thecorrugated sheet portion 33, the inlet side oxidant gas communicationhole 41 a, the outlet side oxidant gas communication hole 41 b, theinlet side fuel gas communication hole 42 a, and the outlet side fuelgas communication hole 42 b, and a second sealing material 53surrounding the outside of the inlet side cooling medium communicationhole 43 a and the outlet side cooling medium communication hole 43 b.

Here, the corrugated portion 33 is a portion corresponding to thereaction surface of the separator, and, among sealing materials, theouter peripheral sealing material 52 surrounding the portioncorresponding to the outer periphery of the corrugated portion 33corresponds to the reaction surface peripheral sealing member.

Note that the sealing material is removed in order to inflow or outflowthe oxidizing gas at portions adjacent to the inlet side oxidant gascommunication hole 41 a and the outlet side oxidant gas communicationhole 41 b. Similarly, in the anode side of the separator (not shown inthe plan view), the sealing material is also removed at portionsadjacent to the inlet side fuel gas communication hole 42 a and theoutlet side fuel gas communication hole 42 b.

Moreover, a nonconductive picture frame-shaped member 61 covering theouter periphery and the outer end face of the whole periphery isarranged at the outer edge portion of the separator 3.

This picture frame-shaped member 61, as shown in FIG. 2, is constitutedby a body portion 61 a having a rectangular section comprising a hardresin material, such as polyamide or PTFE, and a increase and decreaseabsorbing portion 61 b (hereinafter referred to as a flexible absorbingportion) having a trapezoidal section comprising a material softer thanthe body portion 61 a and having resilience, for example, a foammaterial such as rubber.

A border plane 61A between the body portion 61 a and the flexibleabsorbing portion 61 b, and an upper end face 61 bA of the flexibleabsorbing portion 61 b are set at a lower position than upper end faces51A and 53A of the first and second sealing materials 51 and 53, and thedifference of elevation between the upper end face 61 bA and the upperend faces 51A and 53A is set less than a compression margin of the firstand second sealing materials 51 and 53.

The compression margin means a crushing margin at the time of crushingthe first and second sealing materials 51 and 53 when stacking theseparators, so that a predetermined seal surface pressure acts on theseparator 3.

When a concave portion 31 in a separator 3 constituting one fuel cell 1and an other concave portion 31 in a separator 3 constituting an otherfuel cell 1 are put together sequentially, a space having a trapezoidalsection shown in the figure formed between the concave portion 31 of theseparator 3 and the electrode 9 becomes an oxidant gas channel 71 forcirculating the oxidant gas and a fuel gas channel 73 for circulatingthe fuel gas. The space having a hexagonal section shown in the figureformed surrounded by the separators 3 becomes a cooling medium channel75 for circulating the cooling medium.

At the time of stacking the separators, the first and second sealingmaterials 51 and 53 are crushed by the compression margin, so as toreliably seal the periphery of each of the communication holes 41 a, 42a, 43 a, 41 b, 42 b, and 43 b with a predetermined seal surface pressureacting on the separator 3.

At this time, the flexible absorbing portion 61 b of the pictureframe-shaped member 61 arranged at the outer edge portion of eachseparator 3 is also pressed by the separator 3 and compressed by apredetermined dimension, more specifically, by a difference obtained bysubtracting the height difference between the upper end face 61 bA andthe upper end faces 51A and 53A from the compression margin of the firstand second sealing materials 51 and 53.

Therefore, even if the space between separators expands due to theinfluence of heat or the like, the flexible absorbing portion 61 b ofthe picture frame-shaped member 61 is resiliently restored and extendsin the stacking direction of the separators, and follows the bodyportion 61 a of other picture frame-shaped members 61, which are apt toseparate from the flexible absorbing portion 61 b.

Hence, even if the space between separators is enlarged, the pictureframe-shaped members 61 being in contact with each other are notseparated. As a result, foreign substance can be effectively preventedfrom entering from outside, and the durability of the first and secondsealing materials 51 and 53 is also improved.

Since the flexible absorbing portion 61 b is resiliently contractible inthe stacking direction of the separators, relative approach of theseparators 3 is not restricted, so long as this is within a resilientlycontractible range.

Therefore, even if the first and second sealing materials 51 and 53, orthe membrane electrode assembly 5 deteriorates with the lapse of timeand the height becomes low, the flexible absorbing portion 61 b cancontract in the stacking direction of the separators to thereby decreasethe space between separators. As a result, the close contact state ofthese sealing materials 51, 53 and the membrane electrode assembly 3with the separator 3 can be maintained, preventing a decrease in thepower generation performance and a situation that power generation isnot possible

Since the picture frame-shaped member 61 is formed of an insulatingmaterial, there is the effect that a short circuiting does not occur,even if the surface of the fuel cell stack becomes wet due to water orcondensation, and the effect that a short circuiting does not occur dueto a contact of adjacent separators. Furthermore, since the outerperipheral faces of the separator 3 is covered by the insulatingmaterial, it is also possible to prevent adjacent separators from beingshort circuited.

Further, the picture frame-shaped member 61 arranged around the wholeperiphery of the outer edge portion of the separator 3, particularly thebody portion 61 a consisting of a hard resin material, functions as arib for reinforcement. Hence, deformation of a thin metal separator 3can be effectively prevented.

In the case where a thick separator which does not require thereinforcing function is used instead of this thin metal separator 3, thewhole picture frame-shaped member 61 may be constituted of a elasticmaterial.

FIG. 3A is a cross-section showing a modification example of the firstembodiment, and FIG. 3B is a cross-section along a line B-B in FIG. 3A.

In the description for this modification example, the same constituentsas those of FIG. 2 are denoted by the same reference symbols as in FIG.2, and description thereof is omitted.

A picture frame-shaped member 81 in this modification example isconstructed such that a flexible absorbing portion 81 b covers a bodyportion 81 a, and a drain hole 83 is formed in at least one of theflexible absorbing portions 81 b 1 extending parallel with the separator3.

The body portion 81 a and the flexible absorbing portion 81 b areconstituted of, for example, the same material as that of the bodyportion 61 a and the flexible absorbing portion 61 b in FIG. 1.

The drain hole 83 is for discharging excess gas or produced dewcondensation water between separators 3, and is formed curved in anapproximate Z-shape as shown in FIG. 3B, so as to prevent foreignsubstance from entering from outside, by shifting the position ofopenings 83 a and 83 b in the direction of the separator width (in thevertical direction in FIG. 3B).

Also with this modification example, since the picture frame-shapedmember 81 comprises the flexible absorbing portion 81 b, foreignsubstance can be prevented from entering from outside at the time ofenlargement of the space between separators, and a deterioration ofsealability with deterioration of the sealing material with the lapse oftime can be prevented, as in the first embodiment.

The picture frame-shaped member 81 may be connected to a second sealingmaterial 53, as with one arranged on the separator 3 located at thelowest stage in FIG. 3A.

FIG. 18A is a diagram showing the other modification example of thefirst embodiment, and 18B shows a enlarged diagram of the protrudedportion 52 a of the outer peripheral sealing material.

In the explanation of this modification example of the first embodiment,the same constituents as those of FIG. 2 are denoted by the referencesymbols and their explanations are omitted.

In the picture frame-shaped member 261 according to this modificationexample, the flexible absorbing portion 261 b (the insulating outerperipheral member) covers the main body portion 261 a, and the bothsurfaces of the outside portion of the outer peripheral sealing material52 of the separator 3, that is, the front and rear surfaces of theoutside portion is covered by the flexible absorbing portion 261 b.Since the outer peripheral end surface of the separator 3 and the inneredge surface of respective communication holes 41 a,42 a,43 a,41 b, 42b, and 43 b are covered by the picture frame-shaped member 261 and theflexible absorbing portion 261 b, and the inner end surface ofrespective communication holes 41 a, 42 a, 43 a, 41 b, 42 b, and 43 bare covered by the flexible absorbing portion 261 b.

These main body portion 261 a and the flexible absorbing portion 261 bare constituted by the same material as those of the main body portion61 a and the flexible absorbing portion 61 b shown in FIG. 2.

In addition, the flexible absorbing portion 261 b is integrallyconstituted with the first sealing material including the peripheralsealing material 52, and also integrally constituted with the secondsealing material 53.

The peripheral sealing material flat portion 52 b of one of adjacentseparators 3 is formed in a flat shape, and the peripheral sealingmaterial 52 a is formed in a protruded shape. Furthermore, the topportion of the protruded peripheral sealing material is configured toform an R-shape in cross-section.

According to the construction of this modification example, the flexibleabsorbing portion 261 b is capable of elastically contracting in thestacking direction of the separators, it is possible, as described inthe first embodiment, to prevent contamination when the separator spaceis expanded, and also to prevent sealing property of the sealingmaterial due to passage of time.

Sine the outer end surface of the separator 3 and the inner end surfacesof respective communication holes 41 a, 42 a, 43 a, 41 b, 42 b and 43 bare covered by the picture frame-shaped member, it is possible toprevent the electrical short circuiting at the outer end surface of theseparator 3 and the inner end surfaces of the communication holes 41 a,42 a, 43 a, 41 b, 41 b, and 43 b.

In addition, since the exposed metal surface of the separator 3 at theoutside portion of the peripheral sealing material 52 is totally coveredby the flexible absorbing portion 261 b, it is possible to preventadjacent separators to be electrically short circuited while improvingthe corrosion resistance.

Furthermore, since the flexible absorbing portion 261 b is integrallyconstructed with the first sealing material 51 as well as the secondsealing material 53, it is possible to form these materials at the sametime, which results in reducing the manufacturing cost of thesecomponents.

In addition, since the peripheral sealing materials 52 are formed in acombination of a flat shape and a protruded shape, misalignment of theprotruded portion 52 a of the peripheral sealing material 52 a withrespect to the flat portion 52 b of the peripheral sealing material 52 acan be absorbed, which makes it unnecessary to aligning operation of thesealing positions, and which results in increasing the productivity.

At the time of stacking separators, the R-shape cross section of the topportion of the protruded portion of the peripheral sealing material ofone separator is pressed on the flat portion of the sealing material ofanother separator, the sealing is improved.

FIG. 4 is a cross-section showing another modification example of thefirst embodiment.

In the description of this modification example, the same constituentsas those of FIG. 2 are denoted by the same reference symbols as in FIG.2, and description thereof is omitted.

The picture frame-shaped member 91 according to this modificationexample is constructed such that a covering margin L1 of a body portion91 a which covers the reaction plane 3A side of the separator 3 is setto substantially the half of a covering margin L2 which covers thecooling plane 3B side, and a flexible absorbing portion 91 b isintegrated with only the inside edge portion on the cooling plane sideof the body portion 91 a.

The body portion 91 a and the flexible absorbing portion 91 b areconstituted of, for example, the same material as that of the bodyportion 61 a and the flexible absorbing portion 61 b in FIG. 1.

Also with this modification example, since the picture frame-shapedmember 91 comprises the flexible absorbing portion 91 b, foreignsubstance can be prevented from entering from outside at the time ofenlargement of the space between separators, and a deterioration ofsealing capability with deterioration of the sealing material with thelapse of time can be prevented, as in the first embodiment.

Further, the flexible absorbing portion 91 b of the picture frame-shapedmember 91 according to this embodiment has a higher protrusion heightfrom the separator 3 than that of the flexible absorbing portion 61 b inthe first embodiment. As a result, an even greater increase and decreasemargin can be acquired, and hence this has excellent following abilityat the time of enlargement of the space between separators.

A fuel cell according to a second embodiment of the present inventionwill now be described.

FIG. 5 is a cross-section showing the main parts of the fuel cell.

The same constituents as those of FIG. 1 are denoted by the samereference symbols as in FIG. 1, and description thereof is omitted.

A picture frame-shaped member 101 according to this embodiment has adifferent basic construction from that of the first embodiment and themodification examples thereof which use elastic deformation to absorbincrease and decrease, in that increase and decrease in the stackingdirection of the separators is absorbed mechanically.

This picture frame-shaped member 101 has a convex shape in section witha protruding portion 101 a protruding from a base portion 101 b, and theprotruding portion 101 a is arranged so as to face the inside of thefuel cell stack (the right side in FIG. 5) and the outside thereof (theleft side in FIG. 5) alternately along the stacking direction of theseparators.

The adjacent two picture frame-shaped members 101 are normally notbrought into contact with each other on a plane 101B parallel with theseparator 3, but are brought into contact with each other on a plane101A parallel with the stacking direction of the separators.

That is to say, a space between separators is provided by the protrudingheight of first and second sealing materials 51 and 53 (in FIG. 5, onlythe second sealing material 53 is shown) from the separator 3. Thisprotruding height is set larger than the sum of the protruding height ofthe protruding portion 101 a and the protruding height of the baseportion 101 b from the separator 3.

As a result, a gap 103 is formed between the base portion 101 b of oneof the two adjacent picture frame-shaped members 101 and the protrudingportion 101 a of the other picture frame-shaped member 101.

According to this construction, the movement of expanding or contractingthe space between separators is absorbed only by enlarging or narrowingthe gap 103 between the picture frame-shaped members 101, while theplane 101A of one of the two adjacent picture frame-shaped members 101and the plane 101A of the other picture frame-shaped member 101 slidesrelative to each other, without separating from each other.

Therefore, as in the first embodiment, foreign substance can beprevented from entering from outside at the time of enlargement of thespace between separators, and a deterioration of sealability withdeterioration of the sealing material with the lapse of time can beprevented.

In this embodiment, if taking notice of the adjacent two pictureframe-shaped members 101, since the planes 101B parallel with theseparator 3 do not come in contact with each other, any load along thestacking direction of the separators does not occur between these twopicture frame-shaped members 101.

Therefore, the compression load acting on the first and second sealingmaterials 51 and 53 does not disperse into the picture frame-shapedmember 101, thereby enabling effective prevention of a reduction of aseal surface pressure.

FIG. 6 is a cross-section showing a modification example of the secondembodiment.

In the description of this modification example below, the sameconstituents as those of FIG. 2 are denoted by the same referencesymbols as in FIG. 2, and description thereof is omitted.

According to a picture frame-shaped member 111 of this modificationexample, as in the construction in FIG. 5, a surface 111A of one of theadjacent picture frame-shaped members 111 and a surface 111A of theother picture frame-shaped members 111 slide relative to each otherwithout separating from each other, to thereby enlarge or narrow a gap113 between picture frame-shaped members 111. As a result, as in thesecond embodiment, intrusion of foreign substance at the time ofenlargement of the space between separators, a deterioration ofsealability with deterioration of the sealing material with the lapse oftime, and a decrease in the seal surface pressure can be prevented.

In this embodiment, from the point that picture frame-shaped members 111having the same cross-section are arranged at the outer edge portion ofeach separator 3 in the same form, the construction is different in tothat of the second embodiment in which picture frame-shaped members 101having the same cross-section are arranged at the outer edge portion ofeach separator 3 in a different form, that is, with the protrudingdirection of the protruding portions 101 a alternately changed in thestacking direction of the separators.

Hence, in the case where the picture frame-shaped member 111 isintegrally formed at the outer edge portion of the separator 3 byinjection molding, molding is possible with only one kind of mold,thereby enabling a reduction in production cost.

FIG. 7 is a cross-section showing another modification example of thesecond embodiment.

In the description of this modification example below, the sameconstituents as those of FIG. 2 are denoted by the same referencesymbols as in FIG. 2, and description thereof is omitted.

In a picture frame-shaped member 121 according to this modificationexample, a concave portion 123 is formed in the end face on the coolingplane 3B side of the separator 3, and a convex portion 125 having ashape capable of being fitted to the concave portion 123 is protrudinglyformed on the end face on the reaction plane 3A side of the separator 3.

According to this construction, increase and decrease can be absorbed byenlarging or narrowing the gap between the picture frame-shaped members121, while the inner face 123A of the concave portion and the externalface 125B of the convex portion slide relative to each other parallelwith the stacking direction of the separators, without separating fromeach other. Further, since the picture frame-shaped members 121 havingthe same cross-section are arranged at the outer edge portion of eachseparator 3 in the same form, intrusion of foreign substance at the timeof enlargement of the space between separators, a deterioration ofsealability with deterioration of the sealing material with the lapse oftime, and a decrease in the seal surface pressure can be prevented, anda reduction in production cost can be realized, as with the modificationexample of FIG. 6.

Moreover, according to the picture frame-shaped member 121 in thismodification example, if the convex portion 125 of the pictureframe-shaped member 121 arranged in one of the adjacent separators 3 isfitted into the concave portion 123 of the picture frame-shaped member121 arranged in the other separator 3, the relative position of theseparators 3 can be automatically adjusted, thereby enabling animprovement of workability at the time of assembly and maintenance.

That is to say, in this modification example, a separator positioningdevice according to the present invention is constituted by the concaveportion 123 and the convex portion 125.

A fuel cell according to a third embodiment of the present inventionwill now be described.

FIG. 8 is a cross-section showing the main parts of the fuel cell.

The same constituents as those of FIG. 2 are denoted by the samereference symbols as in FIG. 2, and description thereof is omitted.

A picture frame-shaped member 131 according to this embodiment has abowl-like inclined face with an end face 131A on the cooling plane 3Bside of the separator 3 and an end face 131B on the reaction plane 3Aside of the separator 3 inclined with respect to the cooling plane 3Band the reaction plane 3A, with the inner side down (in thecross-section showing the main part in FIG. 8, the right side down).

In this embodiment, the separator positioning device is constituted bythese end faces 131A and 131B.

According to this construction, increase and decrease of the spacebetween separators can be absorbed by relative sliding movement of theend face 131A of one of the adjacent picture frame-shaped members 131and the end face 131B of the other picture frame-shaped member 131,without separating from each other. Moreover, since picture frame-shapedmembers 131 with the same cross-section and with the same shape aredisposed around the outer periphery of the separator 3, the relativeposition of the separators 3 is automatically adjusted. Since thepicture frame-shaped members 131 having the same cross-section arearranged at the outer edge portion of each separator 3 in the same form,intrusion of foreign substance at the time of enlargement of the spacebetween separators, a deterioration of sealability with deterioration ofthe sealing material with the lapse of time, and a decrease in the sealsurface pressure can be prevented, and a reduction in production costand an improvement of workability at the time of assembly andmaintenance can be realized, as in the modification example of FIG. 6.

A fuel cell according to a fourth embodiment of the present inventionwill now be described.

FIG. 9 is a cross-section showing the main parts of the fuel cell.

The same constituents as those of FIG. 2 are denoted by the samereference symbols as in FIG. 2, and description thereof is omitted.

A picture frame-shaped member 141 according to this embodiment is formedof the same elastic material as that of, for example, the flexibleabsorbing member 61 b in FIG. 1, in the form of feathers of an arrow incross-section.

In this picture frame-shaped member 141, the separator positioningdevice is constituted by a triangular groove 143 in section formed onthe end face of the cooling plane 3B side and a triangular protrudingportion 145 in section formed on the end face of the reaction plane 3Aside.

According to this construction, the increase and decrease of the spacebetween separators is absorbed by elastic increase and decrease of thepicture frame-shaped member 141. Also, if the triangular protrudingportion 145 of the picture frame-shaped member 141 arranged on one ofthe adjacent separators 3 in section is fitted into the triangulargroove 143 in section of the other picture frame-shaped member 141arranged in the other separator 3, the relative position of theseparators 3 can be automatically adjusted, and further, the pictureframe-shaped members having the same cross-section are arranged at theouter edge portion of each separator 3 in the same form. As a result,intrusion of foreign substance at the time of enlargement of the spacebetween separators, a deterioration of sealability with deterioration ofthe sealing material with the lapse of time, and a decrease in the sealsurface pressure can be prevented, and a reduction in production costand an improvement of workability at the time of assembly andmaintenance can be realized, as in the construction of FIG. 8.

In the above described constructions in which the picture frame-shapedmembers 61, 81, 91, 101, 111, 121, 131, and 141 are arranged at theouter edge portion of the separator, the outer edge of the separator 3may be folded to form bent portions 3 a, 3 b and 3 c, as shown in FIG.10.

According to this construction, the bent portions 3 a, 3 b and 3 cfunction as a reinforcement rib and a member of preventing disconnectionof the picture frame-shaped members 61, 81, 91, 101, 111, 121, 131, and141. As a result, deformation of the thin metal separator 3 anddisconnection of the picture frame-shaped member 61, 81, 91, 101,111,121, 131, and 141 can be effectively prevented.

A fuel cell according to a fifth embodiment of the present inventionwill now be described.

FIG. 11 is a cross-section showing the main parts of the fuel cell.

The same constituents as those of FIG. 2 are denoted by the samereference symbols as in FIG. 2, and description thereof is omitted.

In this fuel cell, an annular insulating material 201 comprising aresin, rubber or the like, which cover the inner peripheral surfaces andthe inner peripheral end surfaces, is arranged around the inlet sideoxidant gas communication hole 41 a, the inlet side fuel gascommunication hole 42 a, the inlet side cooling medium communicationhole 43 a, the outlet side oxidant gas communication hole 41 b, theoutlet side fuel gas communication hole 42 b and the outlet side coolingmedium communication hole 43 b, formed in the separator 3.

In FIG. 11, only the outlet side fuel gas communication hole 42 b isshown.

According to this construction, a liquid connection by the coolingmedium and an electrical short circuiting between adjacent separators inthe reactant gas channel can be prevented.

Particularly, since a fuel cell according to the present embodiment usesmetal and thin separators, the space between the separators are small,and hence this has a disadvantageous structure in preventing anelectrical short circuiting between separators. Therefore, the effectaccording to this construction is substantial.

Moreover, at the periphery of the communication hole in this thin metalseparator 3, the insulating member 201 functions as a reinforcement rib,and hence the deformation thereof can also be effectively prevented.

Furthermore, since the protruding height of the insulating member fromthe front and back faces of the separator is set such that theinsulating member 201 arranged on one of the adjacent two separators 3does not come in contact with the insulating member 201 on the otherseparator 3, that is, a gap 203 is formed between the insulating members201, increase and decrease of the space between separators can beabsorbed by enlarging or narrowing this gap 203.

Therefore, intrusion of foreign substance at the time of enlargement ofthe space between separators, a deterioration of sealability withdeterioration of the sealing material with the lapse of time, and adecrease in the seal surface pressure can be prevented.

Moreover, insulating members 201 having the same cross-section arearranged around the communication holes of each separator 3 in the sameform. Therefore, when the insulating member 201 is integrally formedwith the separator 3 by injection molding, molding is possible with onlyone kind of mold, thereby enabling a reduction in production cost.

FIG. 12 and FIG. 13 are cross-sections showing modification examples ofthe fifth embodiment.

In the description of this modification example below, the sameconstituents as those of FIG. 2 are denoted by the same referencesymbols as in FIG. 2, and description thereof is omitted.

In the modification example of FIG. 12, an annular insulating member 211comprising the same material and having the same sectional shape, forexample, as that of the picture frame-shaped member 101 in FIG. 5, isarranged around each communication hole 41 a, 42 a, 43 a, 41 b, 42 b,and 43 b. In the modification example of FIG. 13, an annular insulatingmember 221 comprising the same material and having the same sectionalshape, for example, as that of the picture frame-shaped member 111 inFIG. 6, is arranged around each communication hole 41 a, 42 a, 43 a, 41b, 42 b, and 43 b.

According to these constructions, as with the construction in FIG. 11, aliquid connection by the cooling medium and an electrical shortcircuiting between adjacent separators in the reactant gas channel,intrusion of foreign substance at the time of enlargement of the spacebetween separators, a deterioration of sealability with deterioration ofthe sealing material with the lapse of time, and a decrease in the sealsurface pressure can be prevented.

Particularly, in the modification example in FIG. 13, all the insulatingmembers 221 arranged around the respective communication holes 41 a, 42a, 43 a, 41 b, 42 b, and 43 b have the same sectional shape. Therefore,when the insulating member 221 is integrally formed with the separator 3by injection molding, molding is possible with only one kind of mold,thereby enabling a reduction is production cost.

FIG. 14 and FIG. 15 are cross-sections showing other modificationexamples of the fifth embodiment.

In the description of this modification example below, the sameconstituents as those of FIG. 2 are denoted by the same referencesymbols as in FIG. 2, and description thereof is omitted.

In the modification example of FIG. 14, an annular insulating member 231comprising the same material and having the same sectional shape, forexample, as that of the picture frame-shaped member 61 in FIG. 2, isarranged around each communication hole 41 a, 42 a, 43 a, 41 b, 42 b,and 43 b. In the modification example of FIG. 15, an annular insulatingmember 241 comprising the same material, for example, as that of theflexible absorbing 61 b in FIG. 2, and having a guard portion 241 a atone of the open ends is arranged around each communication hole 41 a, 42a, 43 a, 41 b, 42 b, and 43 b.

Also according to these construction, as with the construction in FIG.11, a liquid connection by the cooling medium and an electrical shortcircuiting between adjacent separators in the reactant gas channel,intrusion of foreign substance at the time of enlargement of the spacebetween separators, a deterioration of sealability with deterioration ofthe sealing material with the lapse of time, and a decrease in the sealsurface pressure can be prevented. Further, the production cost at thetime of integrally forming the insulating members 231 and 241 with theseparator 3 by injection molding can be reduced.

A fuel cell according to a sixth embodiment of the present inventionwill now be described.

FIG. 19A is a cross-section showing the main parts of the fuel cell, andFIG. 19B is a enlarged diagram of a protruding portion of the peripheralsealing material 52 a.

In this embodiment, the same constituents as those of FIG. 2 are denotedby the same reference symbols as in FIG. 2, and description thereof isomitted.

In this fuel cell, both surfaces of the outside portion of theperipheral sealing material 52, that is the front and rear surfaces ofthe outside portion is totally covered by the insulating material 271.In addition, the outer peripheral end surface of the separator 3 and theinner peripheral end surfaces of respective communication holes 41 a, 42a, 43 a, 41 b, 42 b, and 43 a are also covered by the insulating member271.

This insulating member 271 is made of elastic and elastic foam materialsuch as rubber and the like, similar to the flexible absorbing portion61 b.

Furthermore, the insulating member 271 is integrally constructed withthe first sealing material 51 including peripheral sealing material 52and is also integrally constructed with the second sealing material 53.

The flat portion 52 b (the flat portion of the insulating member 271 b)of the peripheral sealing material at one side of the adjacent separator3 is formed in flat, and the protruded portion 52 a 8the protrudedportion of the insulating member 271 a) of the peripheral sealingmaterial at another side of the adjacent separator is formed inprotruded. Furthermore, the top portion of the protruded portion of theperipheral sealing material is configured to be semicircular section.

The peripheral portion of the separator 3 and the inner peripheralportion of respective communication holes 41 a, 42 a, 43 a, 41 b, 42 b,and 43 b comprise step portions 3 d, respectively. The peripheralportions 3 a of the separator 3 and the inner peripheral portions ofrespective communication holes 41 a, 42 a, 43 a, 41 b, 42 b, and 43 bare converted to be the reaction surface 3A by these step portions 3 d.A space 273 is provided between the reaction surfaces 3A of theseparator 3.

According to this construction, it is possible to effectively avoidedthe electrical short circuiting between peripheral end portions of theseparator 3 and between the inner peripheral end surfaces of respectivecommunication holes 41 a, 42 a, 43 a, 41 b, 42 b, and 43 a.

In addition, since both surfaces of the exposed metal surface of theseparator 3 at the peripheral sealing material 52 are totally covered bythe insulating member 271, it is possible to improve the corrosionresistance of the separators and to prevent the electrical shortcircuiting between separators 3.

Furthermore, since the insulating member 271 is integrally constructedwith the first sealing material 51 and the second sealing material 53,these insulating materials can be formed simultaneously, and thereby theproduction cost can be reduced.

Since the peripheral sealing materials 52 are formed in combination of aflat shape and a protruded shape, it is possible to absorb the relativemisalignment of the protruded peripheral material with respect to theflat peripheral material, which thereby makes it unnecessary to conductan alignment operation for peripheral sealing materials 52.

In addition, at the time of stacking the separators, the flat portion 52b of the peripheral sealing material is pressed by the semicircular topportion of the protruded peripheral sealing material 52 a, it ispossible to enhance the sealing between these peripheral portions.

In addition, since step portions 3 d provided at the outer edge portions3 d of the separators 3 made of thin metal plates and provided aroundthe communication holes function as a reinforcing rib, deformation ofthe separators 3 can be effectively prevented.

Since the protruded height of the step portion from front and rearsurfaces of the adjacent separators 3 are set so as not to close thepassage to the reaction surfaces 3A, that is, so as to form a space 273,the increase and decrease between adjacent separators 3 can be absorbedby the increase and decrease of the space 273.

Accordingly, it is possible to prevent extraneous materials fromentering into the space when it is expanded, deterioration of thesealing material due to elapse of time, and reduction of the sealingsurface pressure.

FIG. 16 is a cross-section showing a sixth embodiment.

In the description of this modification example below, the sameconstituents as those of FIG. 2 are denoted by the same referencesymbols as in FIG. 2, and description thereof is omitted.

A picture frame-shaped member 251 according to this embodiment isconstructed such that the outer periphery of a body portion 251 aarranged at the outer peripheral portion of the separator 3 is coveredwith a flexible absorbing portion 251 b comprising a vibration isolatingmaterial such as rubber, so that the flexible absorbing portion 251 bhas also a function as a mounting portion to a vehicle body.

Also according to this construction, as with the construction in FIG. 1,intrusion of foreign substance at the time of enlargement of the spacebetween separators and a deterioration of sealability with deteriorationof the sealing material with the lapse of time can be prevented.

Moreover, in the case where the fuel cells 1 are stacked in the lateraldirection (in the horizontal direction) and mounted on a clamp face 300,the flexible absorbing portion 251 b of the picture frame-shaped member251 comes in contact with the clamp face 300 of the fuel cell 1, to alsohave a vibration isolating function. Hence, it is not necessary to mountthe vibration isolating part to the fuel cell stack as a separate body,thereby enabling a cost reduction.

The flexible absorbing portion 251 b comprising the vibration isolatingmaterial may be provided for each fuel cell or for a plurality of fuelcells as a unit.

A modification example shown in FIG. 17 shows a fuel cell stack in whichone flexible absorbing portion 251 b comprising the vibration isolatingmaterial is provided for each fuel cell. In this fuel cell stack, theflexible absorbing portion 251 b comprising the vibration isolatingmaterial and a flexible absorbing portion 251 c comprising the samematerial as that of the flexible absorbing portion 61 b in FIG. 2 arealternately arranged for every other separator 3.

In the above described embodiments and modification examples, theseparator 3 is formed of a stainless steel, but it may be formed of another metal material such as titanium or a carbonaceous material.

As will be apparent from the above description, according to the presentinvention, the following effects can be obtained.

(1) According to the first aspect of the present invention, with respectto a movement enlarging the space between separators, a gap is notformed between the separator and the picture frame-shaped member, andfurther, with respect to a movement narrowing the space betweenseparators, this movement is not restricted by the picture frame-shapedmember. As a result, intrusion of foreign substance at the time ofenlargement of the space between separators and insufficient sealingwith deterioration of the sealing material with the lapse of time can beeffectively prevented, and excellent power generation performance can bemaintained.

(2) According to the second aspect of the present invention, thewideness or narrowness of the space between separators can bemechanically absorbed by relative sliding movement of the pictureframe-shaped members. As a result, intrusion of foreign substance at thetime of enlargement of the space between separators and insufficientsealing with deterioration of the sealing material with the lapse oftime can also be effectively prevented, and excellent power generationperformance can be maintained.

(3) According to the third aspect of the present invention, since theelastic member is capable of resiliently contracting in the stackingdirection of the separators, relative approach of the separators is notrestricted. With respect to an enlargement of the space betweenseparators, the elastic member is resiliently restored and extends inthe stacking direction of the separators, and follows the separator. Asa result, intrusion of foreign substance at the time of enlargement ofthe space between separators and insufficient sealing with deteriorationof the sealing material with the lapse of time can also be effectivelyprevented, and excellent power generation performance can be maintained.

(4) According to the fourth aspect of the present invention,registration of separators is automatically performed at the time ofstacking the separators, and hence workability at the time of assemblyand maintenance can be improved.

(5) According to the invention of claim 5, it is possible to prevent anelectrical short circuiting between adjacent separators, and therebygood power generation performance of the fuel cell stack can bemaintained

(6) According to the sixth aspect of the present invention, it ispossible to improve the corrosion resistance of separators and toprevent the electric short circuiting between adjacent separators, andthereby make it possible to maintain the good power generationperformance.

(7) According to the seventh aspect of the present invention, it ispossible to improve the corrosion resistance of separators and toprevent the electric short circuiting between separators, and therebymake it possible to maintain the good power generation performance.

(8) According to the eighth aspect of the present invention, since it ispossible to absorb the misalignment of the protruded reaction surfaceperipheral sealing member with respect to the flat reaction surfaceperipheral sealing member, the productivity of the fuel cell stack canbe improved.

(9) According to the ninth aspect of the present invention, not only ina single fuel cell, but also between the adjacent fuel cells, increaseand decrease of the space between separators can be followed. As aresult, intrusion of foreign substance at the time of enlargement of thespace between separators and insufficient sealing with deterioration ofthe sealing material with the lapse of time can also be effectivelyprevented, and excellent power generation performance can be maintained.

(10) According to the tenth aspect of the present invention, since it ispossible to effectively prevent the liquid connection by the coolingmedium and an electrical short circuiting between adjacent separators,and hence excellent power generation can be maintained more reliably.

(11) According to the eleventh aspect of the present invention, it ispossible to absorb increase and decrease of the spaces betweenseparators, it is possible to effectively prevent intrusion of foreignsubstance at the time of enlargement of the space between separators,insufficient sealing with deterioration of the sealing material with thelapse of time, and reduction of sealing surface pressure.

(12) According to the twelfth aspect of the present invention, since theincrease and decrease of the spaces between separators can bemechanically absorbed, it is possible to effectively prevent intrusionof foreign substance at the time of enlargement of the space betweenseparators, insufficient sealing with deterioration of the sealingmaterial with the lapse of time, and reduction of sealing surfacepressure.

(13) According to the thirteenth aspect of the present invention,contraction of the spaces between separators can be followed because theelastic material can be contracted elastically in the stacking directionof the capacitors. The expansion of the spaces between separators, sincethe elastic material can elongate by elastic restoration, it is possibleto effectively prevent intrusion of foreign substance at the time ofenlargement of the space between separators, insufficient sealing withdeterioration of the sealing material with the lapse of time, andreduction of sealing surface pressure.

(14) According to the fourteenth aspect of the present invention, it ispossible to effectively prevent the electrical short circuiting at theinner peripheral surfaces of respective communication holes of adjacentseparators, and thereby the fuel cell is capable of good powergenerating performance.

(15) According to the fifteenth aspect of the present invention, it ispossible to absorb the relative misalignment of one insulating membersto the other insulating member by combining a flat member and aprotruded member, and thereby increase the productivity of the fuelcell.

(16) According to the sixteenth aspect of the present invention, it ispossible to absorb the relative misalignment of one insulating membersto the other insulating member by combining a flat member and aprotruded member, and thereby increase the productivity of the fuelcell.

(17) According to the seventeenth aspect of the present invention, sinceit is possible to improve the short circuiting between adjacentseparators, the good power generation performance is maintained.

(18) According to the seventeenth aspect of the present invention, sinceit is possible to integrally construct the reaction surface peripheralsealing member and the insulating member at the same time, and therebythe production cost can be reduced

(19) According to the nineteenth aspect of the present invention, it ispossible to improve the corrosion resistance of separators, and it isalso possible to effectively prevent short circuiting between adjacentseparators. Thus, it is possible to maintain the good generatingperformance.

1. A fuel cell comprising a pair of separators sandwiching a pair ofelectrodes formed on both surfaces of a solid polymer electrolytemembrane, and insulating members provided around communication holesformed in said separators, so as to form a space between the insulatingmembers.
 2. A fuel cell according to claim 1, wherein a space isprovided between two of said insulating members of adjacent separatorsin the stacking direction of the separators.
 3. A fuel cell according toclaim 2, wherein respective insulating members of respective adjacentseparators are formed such that adjacent separators are capable ofrelatively sliding so as to allow increase and decrease of the spacebetween separators while said insulating members are sealing the spacesbetween separators.
 4. A fuel cell according to claim 3, wherein saidinsulating members are made of an elastic material.
 5. A fuel cellaccording to claim 4, wherein inner peripheral surfaces of thecommunication holes are covered by the insulating member.
 6. A fuel cellaccording to claim 5, wherein one of the insulating members of one ofadjacent separators is formed in a flat shape, and another one of theinsulating member of another one of adjacent separators facing to saidone of the flat insulating member is formed in a protruded shape.
 7. Afuel cell according to claim 6, comprising reaction surface peripheralsealing members surrounding reaction surfaces of said separator, whereinone of the reaction surface peripheral sealing member of one separatoramong adjacent separators is formed in a flat shape, while another oneof the reaction surface peripheral sealing member of another separatorsfacing said flat reaction surface peripheral member is formed in aprotruded shape.
 8. A fuel cell according to claim 7, wherein an outsideportion of said reaction surface peripheral sealing member is totallycovered by said insulating member.
 9. A fuel cell according to claim 8,wherein said reaction surface peripheral sealing member and saidinsulating member are integrally formed.
 10. A fuel cell according toclaim 9, wherein both outside surfaces of said reaction surfaceperipheral sealing member are totally covered by the insulating memberwhich is integrally formed with said reaction surface peripheral sealingmember.